This section provides background information related to the present disclosure which is not necessarily prior art.
Reciprocating-piston pumps which are driven by electromagnets and which serve for delivering and dosing fuel are known for example from DE 4328621 and DE 10 2001 111 926 and have been tried and tested.
With the proliferation of fuels with a relatively high fraction of contents not based on mineral oil, such as for example biodiesel or alcohols, and therefore also of water, the materials of the friction partners, in particular of the pistons and of the cylinder, have had to be adapted; nevertheless, under certain operating conditions, new wear phenomena are encountered in such dosing pumps. The wear phenomena are caused for example by local overheating in the event of a locally restricted lubrication film failure, or by the degraded lubrication properties in relation to media based purely on mineral oil.
It is known from documents U.S. Pat. No. 2,337,821 and U.S. Pat. No. 3,153,897 for grooves running both in the circumferential direction and also in the longitudinal direction to be provided on the piston surface, which grooves are suitable for improving the lubrication and, if appropriate, retaining abrasion products in the grooves. The grooves are, in part, connected to the working side of the pump piston by bores.
Documents U.S. Pat. No. 2,231,861, U.S. Pat. No. 2,371,848 and U.S. Pat. No. 5,140,905 also present pumps having axial circumferential grooves to which liquid is supplied via bores.
Document U.S. Pat. No. 2,937,659 presents a pump piston having a check valve received therein, which check valve discharges the delivered volume flow to the pressure side through grooves in the piston.
Document 4644851 presents a compressor in which the piston bearing is assisted by pressure fields to which medium is supplied from the working side of the piston.